Diesel fuel and method of improving diesel fuel ignition



Patented June 19, 1945 DIESEL FUEL AND METHOD OF IMPROVING DIESEL FUEL IGNITION George 0. Curme, Jr., White Plains, N. Y., assignor to Carbide and Carbon Chemicals Corporation, a corporation of New York No Drawing. Application November 28, 1941,

Serial No. 420,816

13 Claims.

This invention relates to improvements in the operation of internal combustion engines of the compression ignition or Diesel type and to improved fuels for such engines. It more especially concerns a novel control of the combustion characteristics of liquid hydrocarbon distillates of the type employed as Diesel fuels, and includes a novel Diesel fuel having blended therein one or more polyethylene or poly 1,2 propylene glycol dinitrates, or certain mixed propylene ethylene glycol dinitrates, which blended product has improved combustion characteristics, a suitably low ignition temperature and a relatlvely high-octane value.

Because/of certain manifest advantages inherent in Diesel type engines, their use in airplanes, locomotives, trucks and busses is rapidly expanding. Such engines provide greater fuel economy, smaller fire hazards, and have higher operating efficiencies than the usual engines of the spark ignition type.

In the operation of Diesel engines a liquid fuel is injected into compressed air within a combustion chamber, and is spontaneously ignited there while under pressure. In order to facilitate the starting and to enhance the smoothness of operation of such engines it is important that the period of delay between the time of iniectlon of the fuel charge and its ignition be reduced to a minimum. Delayed ignition produces in the engine a condition known as knocking, and causes unsatisfactory performance.

A number of processes have been developed for decreasing the ignition delay period of a Diesel fuel in order to improve the ignitability and facilitate the combustion of such fuel in a Diesel engine. Various compounds which have heretofore been proposed for blending with Diesel fuels for the purpose of accelerating the ignition of such fuels, for lowering the temperature and pressure at which spontaneous ignition occurs, and for increasing the rate of flame propagation, have had a distinct modifying effect upon the combustion characteristics of such fuels, but none has proved entirely satisfactory for use with all Diesel fuels.

Among the more important objects of the present invention are: The improvement of the ignition and combustion characteristics of fuels of the Diesel type by the incorporation therein characteristics of the hydrocarbon mixture are improved, the ignition temperature thereof lowered, and the cetane value of the hydrocarbon mixture increased; and the provision of a novel fuel of the Diesel type having a high octane number, and igniting readily and functioning smoothly under service conditions.

The invention is based in important part upon the surprising and important observation that the dinitrates of the polyethylene and poly- 1,2 propylene glycols, and especially of those polyethylene and poly 1,2 propylene glycols and mixed propylene ethylene glycols containing between one and eight ether groups in the molecule, (that is, 1,2 polyglycols containing one or more ether linkages and having the general formula HO'(CnH2nO)x'Cm'H2mOH, where n is 2 or 3, m is 2 or 3, and .r is a whole number from 1 to 8), are extremely effective for increasing the cetane numbers, of Diesel fuels. Of this group, the dinitrates of diethylene glycol, dipropylene glycol, propylene ethylene glycol, triethylene glycol, and tetraethyleneglycol have particular value as combustion and ignition promoters for Diesel fuels. The diethylene glycol dinitrate has outstanding merit, and generally is preferred.

In the preferred practice of the present invention there is blended with a Diesel fuel a small amount, usually from around 0.2% to around 5%, of a dinitrate derivative of a polyethylene or polypropylene glycol or propylene ethylene glycol of the class named. The polyglycols used in making the dinitrate derivatives may be produced by reacting ethylene or propylene glycol or polyglycol with ethylene oxide or propylene oxide in well-known manner. Among the additives contemplated by this invention are the dinitrates of diethylene glycol, triethylene glycol, tetraethylene glycol; the higher polyethylene glycols, such as octaethylene glycol; the polypropylene glycols, such as dipropyl'ene glycol and tripropylene glycol; and the mixed propylene ethylene polyglycols. A representative Diesel fuel with which the selected polyglycol dinitrate may be blended is a petroleum distillate commonly marketed as a Diesel fuel oil, and having a flash point of 230 F., a cetane number of around 39, and a specific gravity at 60/60 F. of 0.873.

Diethyleneglycol dinitrate may be produced triethylene glycol with a mixed nitrating acid hereinafter described, in a ratio by weight of mixed acid to the'glycol of 2.6, is a clear substantially neutral liquid having a specific gravity of 1.327 at 20 C. Tetraethylene glycol dinitrate, produced in similar manner by reacting tetrataining the temperature between 10 'arai 15 C. After all of the polyglycol has been added, the mixture is agitated for thirty minutes, cooled to 5 C., and dumped into a large excess of ice water. The polyglycol dinitrate layer is separated, washed several times with distilled water, and then washed several times with a 2% aqueous solution of sodium carbonate. It then is finally washed with water until neutral to litmus. The product is then dried in contact with anhydrous sodium sulfate, and is filtered.

The mixed acid used in preparing the dinitrates of the polyglocols generally contains around 50% of nitric acid and 5% of water, the balance being sulfuric acid. A molar ratio of nitric acid to polyglycol within the range between 1.0 and 4.0

conveniently is used.

The examples represented in the accompanying table serve to illustrate the effectiveness of the po y lycol dinitrates of the invention in increasing the cetane number of Diesel fuels. In preparing the blended fuel stock, the particular polyglycol dinitrate indicated in the table was intimately mixed or blended with the respective typical Diesel fuels, such fuels being identified as follows:

ethylene glycol with such mixed acid in an Fuel A mm] 3 r1161 0 Fuel 1)- acidzglycol weight ratio of 2.02, is a substantially neutral liquid having a specific gravity of 1.286 specific e oo/ o F o. 876 0. 873 0' 886 848 at 20 C. A mixture of the higher polyethylene Flesh Pp closed cup 1 0 0 230 1 glycol dinitrates may be produced in like manner Dim g g mggi Cetane Cetane I Cetene me] Compound added an cent number of number of number by g a fuel the blend increase Ethyl nitrate 1 1. 5 26. 6 45. 6 20. 0 Ethylene glycol dinitrate 1. 5 25. 6 35. 4 9. 8 Propylene glycol dinitrate 1.15 25. 6 37. 6 l2. 0 Diethylene glycol dlnitra 1.5 25. 6 50.8 25. 2 Triethylene glycol dinitrate 1. 5 25. 6 54. 0 28. 4 etraethylene glycol dinitrate. 1. l 25. 6 48. 9 23. 3 Polyethylene g ycol "400" dinitrate 0. 7 25. 6 41. 3 l5. 7 Diethylene glycol dinltrate 0,8 38. 9 56. 7 1 l7. 8 Triethylene glycol dinltrate 0. 6 38. 9 60. 2 21. 3 Diethylene g yeol dinitratenfl 1. 3 34. 4 52. 8 l8. 4 Triethylene glycol dinitrate- 1. 0 34. 4 53. 5 l9. 1 Tetraethylene glycol dlnitratc. 0. 8 34. 4 53. 1 18. 7 Ethylene glycol dlnitrate 1. 0 30. l 40. 8 1. 7 Propylene glycol dinitrate l. 0 39. 1 41. 3 2. 2 Dlethylene glycol dinitrate 0. 7 30. 1 48. 8 9. 7

1 For comparison 1 Polyethylene glycol "400" is a mixture of polyethylene glycols having an average molecular weight around 400.

by nitrating with the aforesaid'mixedacid the mixture of polyethylene glycols'having an average molecular. weight of approximately 400, formed by reacting ethylene glycol or diethylene glycol with ethylene oxide at an elevated temperature and pressure, washing and neutralizing the resultant. reaction mixture, and stripping therefrom the fluids distillable at 150 C. under an absolute pressure around 3.5 mm. of mercury. The nitrated product is a substantially neutral liquid having a specific gravity of 1.281 at 20 C. The dinitrates of the polypropylene glycols can be prepared in generally similar manner somewhat less conveniently.

In general, -in the preparation of the polyglycol dinitrates, the mixed nitrating acida mixture of nitric acid, sulfuric acid and wateris placed in a reaction vessel, which may be of stainless steel or glass, and is fitted with an agitator. a cooling brine coil, and a glycol feed The ignition quality of the base stock or Diesel fuel, and that of each fuel blend, was determined by comparison with a standard reference fuel in a service engine provided with means for controlling all operation variables, using the ignition delay method. The values obtainedin the tests are expressed in the table in terms of cetane number, and were determined by the well-known method described in Proc. Am; Soc. Testing Materials, vol. 36, I,'page 416 (1936). An increase in cetane number indicates an improvement in the combustion characteristics of the fuel blend.

It will be observed from the table that the addition of less than 1% by volume of diethylene glycol dinitrate to certain high cetane Diesel fuels (see fuel D) increases the cetane number of such fuels up to five or more times as much as 1% of ethylene glycol dinitrate, and over four times as much as 1% ofpropylene glycol dinitrate.

In the case of Diesel fuels of lower cetane number (see'fuel A), the table indicates that, calculated on the basis of the addition of 1.5% by volume of the additive to the Diesel fuel, di-

ethylene glycol dinitrate and the higher polyethylene glycol dinitrates increase the cetane numbers of the fuels considerably over 2.5 times the increases secured by the use of ethylene glycol dinitrate, and considerably over 2 times that evidenced by the increase in cetane number of the in fuel-by the admixture therewith of certain polyglycol dinitrates of the invention. The fuel used, and designated in the table as Diesel fuel E, was-Sun No. 2 furnace oil, marketed by The Sun Oil 'Co., and commonly used as a Diesel fuel: 1.)

appearing in the claims, are intended to desi nate any liquid hydrocarbon fuel adapted for use in internal combustion engines of the Diesel or compression ignition type.

The term polyethylene glycol, as used in the claims, is intended to include diethylene glycol and the higher polyethylene glycols, as well as mixtures of such glycols; and the term polypropylene glycol is intended to include dipropylene glycol and the higher polypropylene glycols, and mixtures thereof.

I claim:

1. An improved Diesel fuel comprising a fuel oil having present therein a small proportion of a dinitrate of a poly 1,2 alkylene glycol having The data presented in this table evidences the outstanding value of these polyglycol dinitrates for improving the ignition properties of Diesel 30 fuels. The polypropylene glycol dinitrates and the mixed propylene ethylene glycol dinitrates are much more soluble in Diesel fuels than the corresponding polyethylene glycol dinitrates. Thus, in

the aforesaid Diesel fuel E, at C., dipropylene 5 glycol dinitrate is around four times as soluble, and propylene ethylene glycol dinitrate is over twice as soluble, as diethylene glycol dinitrate.

These very satisfactory solubility characteristics of the polyglycol dinitr'ates of the invention become particularly important where the blended Diesel fuel is intended for use under low temperature conditions.

When using in the practice of the invention those higher polyethylene glycol dinitrates that are of limited solubility in the Diesel fuel being improved, a suitable solvent for the selected glycol dinitrate which is miscible with or soluble in the Diesel fuel may be used for increasing the amount of the polyglycol dinitrate soluble in the fuel. Such solvent should not lower the flash-point of the fuel below 150 F., and should not greatly increase the pour point of the fuel. The latter preferably should not be higher than 50 F.

lsophorone is an example of such a mutual ,solvent.

As already indicated, there may be substituted,

for all or a selected portion of the aforesaid polyethylene or polypropylene glycol dinitrates, the

mixed propylene ethylene polyglycol dinitrates.

Such a compound may be made by nitrating the asymmetrical propylene ethylene glycol. The latter may be prepared by reacting one mol or less of propylene oxide with one mol of ethylene glycol or of a polyethylene glycol, for example at temperatures ranging between and 70 C., and at pressures ranging up to around pounds per square inch (gauge). Methods for making the asymmetrical polyglycols, such as propylene ethylene glycol, are disclosed in British Patent 393,753 to Naamlooze Vennootschap. The presence of a propylene group or groups in the molecule tends to increase the solubility of the dinitrate in the usual types of Diesel fuels. 75

The term Diesel fuel," and similar expressions the general formula HO- (CnHznOh-CmHmiOI-I. wherein'n is 2 or 3, m is 2 or 3, and a: is a whole number from 1 to 8, effectively decreasing the ignition delay period of the fuel.

2. An improved Diesel fuel comprising a fuel oil having present therein a small proportion of a dinitrate of a polyethylene glycol effectively decreasing the ignition delay period of the fuel.

3. An improved Diesel fuel comprising a fuel oil having present therein a small proportion of a dinitrate of a polyethylene glycol having at least four carbon atoms in the molecule, and effectively decreasingthe ignition delay period of the fuel.

4. An improved Diesl fuel comprising a fuel oil having present therein a small proportion of diethylene glycol dinitrate effectively decreasing the ignition delay period of the fuel.

5. An improved Diesel fuel comprising a fuel oil having present therein a small proportion of triethylene glycol dinitrate effectively decreasing the ignition delay period of the fuel.

6. An improved Diesel fuel comprising a fuel oil having present therein a small proportion of a dinitrate of a poly(l,2-propylene)' glycol effectively decreasing the ignition delay period of the fuel.

7. The method of accelerating the ignition of liquid Diesel fuels in an internal combustion engine of the compression ignition type, which comprises admixing with the fuel, prior to its injection into the cylinder of the engine, a small proportion of a dinitrate of a poly 1,2 alkylene glycol having the general formula portion of apolyethylene glycol dinitrate in amount substantially decreasing the ignition del'ay period of the fuel.

'9. The method of accelerating the ignition of liquid Diesel fuels in an internal combustionengine of the compression ignition type. which comprises admixing with the fuel, prior to its injection into the cylinder of the engine, a small proportion of a dinitrate of a polyethylene glycol having at least four carbon atoms in the molecule, said glycol dinitrate being blended with the fuel in amount substantially decreasing the ignition delay period of the fuel.

10. The method of accelerating the ignition of liquid Diesel fuels in an internal combustion engine of the compression ignition type, which comprises admixing with the fuel, prior to its injection into the cylinder of the engine, a small proportion of diethylene glycol dinitrate in amount substantially decreasing the ignition delay period of the fuel.

ill. The method of accelerating the ignition of liquid Diesel fuels in an internal combustion engine of the compression ignition type, which comprises admixing With the fuel, prior to its injection into the cylinder of the engine, a small proportion of triethylene glycol dinitrate in amount substantially decreasing the ignition delay period of the fuel.

12. The method of accelerating the ignition of liquid Diesel fuels in an internal combustion engine of the compression ignition type, which comprises admixing With the fuel, prior to its injection into the cylinder of the engine, a small proportion of a poly(1,2-propylene) glycol dinitrate in amount substantially decreasing the ignitiondelay period of the fuel.

13. The method of accelerating the ignition of liquid Diesel fuels in an internal combustion engine of the compression ignition type, which comprises admixing with the fuel, prior to its injection into the cylinder of the engine, a small proportion of di(1,2-propylene) glycol dinitrate in amount substantially decreasing the ignition de- 20 lay period of the fuel.

GEORGE O. CURME, JR. 

